Generator systems for aircraft may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. Each generator includes rotors mounted on a common rotatable shaft. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are fed to a regulator or a control device, which in turn outputs a DC current. Next, the DC current is provided to stator windings of the exciter. As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator windings, and this three-phase AC output can then be provided to a load such as, for example, an aircraft electrical system.
In recent years, the demand for lower weight, higher power generators capable of rotating in a speed range of 12,000 rpm to 24,000 rpm has increased. To meet these demands, generators now incorporate rotors having larger diameters than previously used rotors. However, a larger rotor may cause the generator to reach its lowest speed resonance value while rotating at a speed lower than desired, for example, at speeds of less than 12,000 rpm. To counteract this phenomenon, the rotor may be mounted to a stiffer, lighter shaft, which can shift the lowest speed resonance to a higher value to allow the rotor to rotate at a higher speed.
Current shafts, however, are not suitable for incorporation into high power generators. In particular, the shafts typically have thin walls and do not have a stiffness that is sufficient to shift the lowest speed resonance of a rotor to a desired value. Additionally, the cost associated with manufacturing these shafts is relatively high. Consequently, implementing these shafts into a generator may not be economically feasible.
Therefore, there is a need for a shaft that is suitable for incorporation into high power generators. Additionally, there is a need for a shaft that is sufficiently stiff and light to shift the lowest speed resonance of a generator to a desired value. Moreover, a relatively inexpensive method for manufacturing the shaft is needed. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.